High-pressure discharge lamps, in particular so-called HID lamps, have been known for a long time. They are used for various purposes, and above all for applications in which relatively good color rendering and very good luminous efficiency are required. These two properties are usually in conflict, i.e. improving one property degrades the other, and vice versa. The color rendering is generally more important for general lighting applications, but the situation is reversed for example in street lighting.
High-pressure discharge lamps are furthermore distinguished by a high power in relation to the size of the lamp or the size of the light-emitting region.
Here and in what follows, high-pressure discharge lamps are intended to mean only those lamps which have electrodes inside the discharge vessel. There are very many publications and an enormous amount of patent literature on the subject of high-pressure discharge lamps, for example WO 99/05699, WO 98/25294, and Born, M., Plasma Sources Sci. Technol., 11, 2002, A55.
DE Application 10 2006 034 833.8, which has not yet been published, discloses a molecular radiation-dominated high-pressure discharge lamp. With noncritical selection of the rare earth iodides, however, the problem of a sensitive power dependency of the color distance ΔC(P) in the event of a power variation often arises. The color distance is also referred to as the color difference or color deviation. Minor differences in the power from the working point with ΔC=0 lead to sizable ΔC values, which change very rapidly with an increasing power from positive to negative values or vice versa.